Structure and process for w contacts

ABSTRACT

Structures and processes include a single metallization step for forming a metal nitride liner layer suitable for contact formation. The structure and processes generally includes forming a nitrogen-enriched surface in a deposited metal liner layer or forming a nitrogen-enriched surface in the dielectric material prior to deposition of the metal liner layer. In this manner, nitridization of the metal occurs upon deposition of nitrogen ions into the metal liner layer and/or as a function of additional conventional processing in fabricating the integrated circuit such that the deposited nitrogen ions diffuse into at least a portion of the metal liner layer. As a consequence, only a single metal layer deposition step is needed to form the metal liner layer.

DOMESTIC PRIORITY

This application is a DIVISIONAL of U.S. patent application Ser. No.14/945,754, filed Nov. 19, 2015, the disclosure of which is incorporatedby reference herein in its entirety.

BACKGROUND

The present invention generally relates to semiconductor integratedcircuits, and more particularly, to the structure and formation of linerstructures that create insulation and diffusion barriers of a tungstenmetal contact.

An integrated circuit (IC) generally includes a semiconductor substratein which a number of device regions are formed by diffusion or ionimplantation of suitable dopants. This substrate usually involves apassivating and an insulating layer required to form different deviceregions. The total thickness of these layers is usually less than onemicron. Openings through these layers (called vias or contact holes)allow electrical contact to be made selectively to the underlying deviceregions. A conducting material is used to fill these holes, which thenmake contact to semiconductor devices.

In its simplest form, a via may be formed by first masking an insulatinglayer, e.g., a dielectric layer, with photoresist and then selectivelyetching a portion of the insulating layer. The via is etched through anopening formed in the photoresist using well known photolithographictechniques, to form an opening to the underlying conductive layer.Depending on the aspect ratio and the interconnection ground rules,isotropic or anisotropic etching processes may be used to form a hole inthe dielectric.

After the via etch, and photoresist removal, it is possible to deposit aconductive layer in the via. Conductive material is deposited in the viato form the electrical interconnect between the conducting layers.However, a liner layer is usually desirable between the insulating andconductive layers.

The presence of a liner layer on the sidewalls of the via is desirablebecause structural delamination and conductor metal diffusion can occurunless there is a layer of protection, a liner layer, between theconductive layer and the etched insulating layer. For structuralintegrity, the liner layer should line the entire side wall and willgenerally cover the bottom of the via as well.

The liner and conductive layers may be deposited by sputtering, CVD,electroless deposition and electrodeposition. Rf bias sputtering, ingeneral, is known in the art and involves the reemission of materialduring the sputter deposition thereof through the effects of attendantion bombardment of the layer being deposited. In effect, Rf biasedsputtering is the positive ion bombardment of a substrate or film duringits deposition. Therefore, during Rf bias sputtering, there is alwayssimultaneous etching and deposition of the material being deposited.Previously deposited layers are not etched as part of a standard Rfbiased sputter deposition.

High quality contacts are essential to high device yield andreliability, but fabrication of these high quality contacts posesseveral technical challenges. For example, the contacts are designed tohave a high ratio of the height to the diameter, known as the aspectratio. High aspect ratio is a consequence of several constraints in thedesign of the IC.

For example, it is desirable to achieve a high packing density of thecontacts to enable high circuit density. This constrains the diameter ofthe contacts to be as small as possible. In addition, the dielectricseparating the semiconductor devices from the first metal level must bethick enough to protect transistors. The contacts often span thethickness of dielectric over a transistor and transistor gate over thesubstrate. These constraints lead to contacts with aspect ratios largeenough to present manufacturing challenges.

As integrated circuit technology become smaller, the large aspect ratiocombined with very small geometries creates many manufacturing andperformance issues. Current attempts to manufacture very small contactshave been plagued with very high resistance. These contact resistancescan dominate integrated circuit performance particularly with smallprocess geometries such as thirty-two nanometers.

The dielectrics used for the insulating layers are typically comprisedof silicon dioxide, a thermosetting polyarylene resin, an organosilicateglass such as a carbon-doped oxide (SiCOH), or any other type of hybridrelated dielectric.

The liner can be a single layer or multiple layers and is not located onthe bottom horizontal surface of the via. The liner is comprised of ametal such as, for example, Ta, Ti, Ru, Ir, Co, and W, and/or a metalnitride such as TaN, TiN, and WN. An optional adhesion layer, notspecifically shown, can be used to enhance the bonding of the liner tothe dielectric layer.

Current processes for depositing the liner generally include a two-stepprocess, which includes a first step of depositing a metal followed by asecond step of depositing a metal nitride layer. The two step processfor depositing two metal layers is inherently inefficient since it is atwo-step process and affects throughput. Moreover, because two layersare deposited, thickness control becomes an issue especially as devicedimensions shrink. For example, for 32 nm node device fabrication, thethickness of each layer defining the liner layer is on the order ofabout 20 Angstroms (Å) for a total thickness of about 40 Å. Smallerthicknesses will be required for future device fabrication, which willbe difficult given the relatively high deposition rates utilized toproduce individual layer thicknesses at or less than 20 Å.

SUMMARY

The present invention is generally directed to methods for forming anintegrated circuit and contact structures for an integrated circuit.

In one embodiment, a method for forming an integrated circuit comprisesproviding a patterned substrate comprising a contact hole in adielectric layer, wherein the contact hole includes sidewalls formed ofthe dielectric layer and a bottom surface defined by a source or drainregion or a metal gate; conformally depositing a single metal linerlayer onto the patterned substrate; generating nitrogen ions from anitrogen containing gas selected from the group consisting of nitrogen(N₂) and ammonia (NH₃); exposing the metal liner layer to form anitrogen enriched metal liner layer; and depositing a tungsten metalinto the contact hole.

In another embodiment, method for forming an integrated circuitcomprises providing a patterned substrate comprising a contact hole in adielectric layer, wherein the contact hole includes sidewalls formed ofthe dielectric layer and a bottom surface defined by a source/drainregion or a metal gate; generating nitrogen ions from a nitrogencontaining gas selected from the group consisting of nitrogen (N₂) andammonia (NH₃); exposing the substrate including the dielectric layer toform a nitrogen enriched dielectric layer at about a surface of thedielectric layer; conformally depositing a single metal liner layer ontothe patterned substrate and forming a metal nitride at an interfacebetween the single metal liner layer and the nitrogen enricheddielectric layer and into at least a portion of the metal liner layer;and depositing a tungsten metal into the contact hole.

A contact structure for an integrated circuit device comprises apatterned dielectric material comprising at least one contact hole, thecontact hole including a bottom surface, and sidewalls extending fromthe bottom surface to a top surface, wherein the bottom surface isdefined by a source/drain region or a metal gate; a self-formed metalnitride liner layer on the sidewalls and the bottom surface of the atleast one contact hole; and a tungsten plug disposed within the at leastone contact hole.

In another embodiment, the contact structure for an integrated circuitdevice comprises a patterned dielectric material comprising at least onecontact hole, the contact hole including a bottom surface, and sidewallsextending from the bottom surface to a top surface, wherein the bottomsurface is defined by a source/drain region or a metal gate, and whereinthe dielectric material is enriched at least at the sidewalls of thecontact hole; a metal liner layer disposed on the sidewalls and thebottom surface of the at least one contact hole, wherein contact of themetal liner layer with the enriched dielectric material forms a metalnitride gradient in the metal liner layer; and a tungsten plug disposedwithin the at least one contact hole.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with advantagesand features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1A depicts a schematic cross-sectional view illustrating a contacthole formed in an interlevel dielectric layer according to an embodimentof the present invention;

FIG. 1B depicts a schematic cross-sectional view illustrating thestructure of FIG. 1A after formation of a titanium metal liner layer;

FIG. 1C depicts a schematic cross-sectional view illustrating thestructure of FIG. 1B after deposition of nitrogen ions onto the titaniummetal liner layer;

FIG. 1D depicts a schematic cross-sectional view illustrating thestructure of FIG. 1C subsequent to formation of a tungsten plug withinthe contact hole;

FIG. 2A depicts a schematic cross-sectional view illustrating a contacthole formed in an interlevel dielectric layer according to an embodimentof the present invention;

FIG. 2B depicts a schematic cross-sectional view illustrating thestructure of FIG. 2A after deposition of nitrogen ions onto thedielectric layer to form a nitrogen enriched dielectric layer;

FIG. 2C depicts a enlarged cross-sectional view illustrating thestructure of FIG. 2B after deposition of a titanium metal line layer onall of the exposed surfaces including the bottom surface of the contacthole;

FIG. 2D depicts a schematic cross-sectional view illustrating thestructure of FIG. 2B after deposition of a titanium metal line layer onall of the exposed surfaces including the bottom surface of the contacthole; and

FIG. 2E depicts a schematic cross-sectional view illustrating thestructure of FIG. 2B after deposition of a titanium metal line layer onall of the exposed surfaces with the exception of the bottom surface ofthe contact hole.

The detailed description explains the preferred embodiments of theinvention, together with advantages and features, by way of example withreference to the drawings.

DETAILED DESCRIPTION

The present invention provides a structure and process including asingle metallization step for forming a metal liner layer suitable forcontact formation. The structure and processes generally includesforming a nitrogen-enriched surface in a deposited metal liner layer orforming a nitrogen-enriched surface in the dielectric material prior todeposition of the metal liner layer. In this manner, nitridization ofthe metal occurs upon treatment of nitrogen ions into the metal linerlayer and/or as a function of additional conventional processing infabricating the integrated circuit such that the treated nitrogen ionsdiffuse into at least a portion of the metal liner layer. As aconsequence, only a single metal layer deposition step is needed to formthe metal liner layer as opposed to the prior art's use of two metaldeposition steps. Moreover, improved thickness control is realized sinceonly one metal layer is deposited, which is especially advantageous asthe art transitions to smaller device dimensions.

For ease in understanding and for example only, reference herein will bemade to a titanium metal and nitridization thereof so as to form atitanium nitride liner layer. However, it should be apparent that othermetals are suitable including, but not limited to, tantalum (Ta),titanium (Ti), ruthenium (Ru), iridium (Ir) tungsten (W), cobalt (Co)mixtures thereof, and the like. The metal liner layer serves as abarrier to prevent conductive material from diffusing through and can beformed by a deposition process such as, for example, atomic layerdeposition (ALD), chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition (PECVD), sputtering, chemical solutiondeposition, or plating. The thickness of the metal liner layer may varydepending on the exact means of the deposition process as well as thematerial employed.

In one embodiment, the process generally includes depositing a titaniummetal liner layer at a thickness of less than 40 Angstroms followed bysurface treatment of the titanium metal liner layer with a nitrogencontaining gas to form a nitrogen enriched titanium metal surface.Nitrogen enrichment of the titanium metal forms titanium nitride Ti(N).As defined herein, the nitrogen-containing gas is selected from thegroup consisting of nitrogen (N₂) and ammonia (NH₃). Upon exposure to asuitable energy source, the nitrogen or ammonia dissociates to formnitrogen ions, which are then utilized to enrich a contact surface.Suitable energy sources include but are not limited to thermal energysources and plasma energy sources.

Plasma nitridization generally includes exposing the nitrogen-containingto a plasma effective to generate nitrogen ions. The substrate includingthe titanium metal liner layer or the dielectric layer are then exposedto the nitrogen ions to form a nitrogen enrich surface that alsopenetrates the respective surface to form a nitrogen enriched gradientin the titanium metal liner layer. Subsequent fabrication of the devicefacilitates additional nitrogen diffusion within the titanium metalliner layer or from the dielectric surface to the titanium metal linerlayer to form a titanium nitride (TiN) liner layer. The processtemperature is between 80 to 400° C., and the bias is between 100 to 900W.

Thermal nitridization provides a similar effect as plasma nitridizationbut generally includes exposing the substrate to a temperature effectiveto generate nitrogen ions from the nitrogen containing gas. Again, thenitrogen ions contact and penetrate the surface of the titanium metalliner layer or the dielectric layer so as to form a nitrogen enrichedgradient in the titanium metal liner layer or dielectric layer.Subsequent conventional fabrication of the device facilitates furtherdiffusion within the titanium metal liner layer or from the dielectriclayer to the titanium metal liner layer so as to form a titanium nitrideliner layer. The process temperature is between 200 to 400° C.

Referring now to FIG. 1A-1D, there is shown a process and resultingstructure for forming a titanium nitride liner layer for a tungstencontact structure in accordance with an embodiment. As shown in FIG. 1A,the process generally includes first forming contact holes 14 in aninterlevel dielectric layer (ILD) 12 deposited on a substrate 10 throughconventional lithography and etching processes. The lithographic stepincludes applying a photoresist to the surface of the dielectric layer,exposing the photoresist to a desired pattern of radiation, anddeveloping the exposed resist utilizing a conventional resist developerto form a pattern. The etching process may be a dry etching or wetetching process.

The term “wet etching” generally refers to application of a chemicalsolution. This is preferably a time controlled dip in the etch solution.Preferred etch solutions include HNO₃, HCL, H₂SO₄, HF or combinationsthereof.

The term “dry etching” is used here to denote an etching technique suchas reactive-ion-etching (RIE), ion beam etching, plasma etching or laserablation. During the etching process, the pattern is first transferredto the dielectric layer. The patterned photoresist is typically, but notnecessarily, removed from the structure after the pattern has beentransferred into the dielectric film. The patterned feature formed intothe dielectric material includes the contact holes.

The dielectric layer 12 may comprise any dielectric including inorganicdielectrics or organic dielectrics. The dielectric material 12 may beporous or non-porous. Some examples of suitable dielectrics that can beused as the dielectric material include, but are not limited to: SiO₂,silsesquioxanes, carbon doped oxides (i.e., organosilicates) thatinclude atoms of Si, C, O and H, thermosetting polyarylene ethers, ormultilayers thereof. The term “polyarylene” is used to denote arylmoieties or inertly substituted aryl moieties which are linked togetherby bonds, fused rings, or inert linking groups such as, for example,oxygen, sulfur, sulfone, sulfoxide, carbonyl and the like. The ILD maybe deposited by PECVD procedures as is generally known in the art. Thesepatterned features correspond to the subsequent interconnect vias (i.e.,metal plugs between levels) and can be aligned with underlying sourceand/or drain regions or over a metal gate structure defined by theparticular substrate 10.

Referring now to FIG. 1B, after removal of the photoresist used tocreate the contact holes 14 via plasma ashing and wet cleaning, atitanium metal liner layer 16 is conformally deposited onto thesubstrate including the exposed dielectric surfaces defining the contacthole and the underlying exposed source/drain or metal gate regions. Thetitanium metal liner layer may be deposited through conventionaldeposition processes such as, for example, a plasma vapor depositionprocess such as R.F. sputtering. The thickness of the deposited titaniummetal liner layer is between 10 Å and 40 Å. The titanium metal linerlayer is used to provide adhesion between subsequent overlyingstructures, such as a tungsten plug structure, and ILD layer 12, as wellas supplying the needed titanium, for subsequent formation of a titaniumsilicide layer, if desired.

In FIG. 1C, the patterned substrate with the titanium metal liner layer16 is exposed to nitrogen ions generated from the nitrogen containinggas 18 to form a nitrogen enriched titanium metal liner layer 20. Asdescribed above, generation of the nitrogen ions can be plasma orthermally generated, wherein the nitrogen ions penetrate into at least aportion of the titanium metal liner layer. In one embodiment, thenitrogen ions penetrate into the titanium metal liner layer 16 at adepth of about 75 percent of the thickness of the titanium metal linerlayer; in other embodiments, the nitrogen ions penetrate into thetitanium metal liner layer 16 at a depth of about 50 percent of thethickness of the titanium metal liner layer; and in still otherembodiments, the nitrogen ions penetrate into the titanium metal linerlayer 16 at a depth of about 25 percent of the thickness of the titaniummetal liner layer.

The nitrogen enriched titanium metal liner layer forms titanium nitride(Ti(N)) 20 in the areas where the nitrogen ions have penetrated, whichgenerally includes coating the sides of contact hole 14 and thesource/drain regions or metal gate structure defined by the underlyingsubstrate 10, exposed at the bottom of the contact hole. Moreover,subsequent processing such as a rapid thermal anneal step to create ametal silicide layer or the like can further effect diffusion of thenitrogen ions within the titanium metal liner layer to form asubstantially uniform titanium nitride layer.

Turning now to FIG. 1D, a conductive metal such as tungsten is thendeposited onto substrate including the contact hole to form theso-called tungsten plug 22. By way of example, a conformal LPCVDprocedure at a temperature between about 400 to 500° C. can be used todeposit the tungsten layer to a thickness between about 2000 Å to 9000Å. The reactants, as well as the by-products, of the tungstendeposition, performed using silane and tungsten hexafluoride, cannotattack underlying materials, now protected by titanium nitride layer.

A chemical mechanical polishing (CMP) procedure is next used to removethe regions of tungsten, and the regions of titanium nitride layer 20residing on the top surface of ILD 12. In addition to removal of theunwanted regions of material, via a CMP procedure, the removal procedurecan also be accomplished via a blanket reactive ion etch (RIE) procedure(without the use of photolithographic procedures) using a suitableetchant.

In another embodiment shown in FIGS. 2A-D, a patterned dielectric layeris exposed to nitrogen ions generated from the nitrogen containing gasto form a nitrogen enriched dielectric layer. A titanium metal linerlayer is then deposited onto the nitrogen enriched dielectric layer,wherein the nitrogen ions diffuse into the titanium metal liner layer toform titanium nitride.

Turning now to FIG. 2A, the process generally includes first formingcontact holes 54 in an interlevel dielectric layer (ILD) 52 deposited ona substrate 50 through conventional lithography and etching processes.As previously disclosed, the dielectric layer 54 may comprise anydielectric including inorganic dielectrics or organic dielectrics andmay be porous or non-porous. Some examples of suitable dielectrics thatcan be used as the dielectric material include, but are not limited to:SiO₂, silsesquioxanes, carbon doped oxides (i.e., organosilicates) thatinclude atoms of Si, C, O and H, thermosetting polyarylene ethers, ormultilayers thereof. These patterned features, i.e., contact holes 54,correspond to the subsequent interconnect vias (i.e., metal plugsbetween levels) and can be aligned with underlying source and/or drainregions or over a metal gate structure defined by the particularsubstrate 50.

Referring now to FIG. 2B, after removal of the photoresist used tocreate the contact holes 54 via plasma ashing and wet cleaning, thedielectric layer 52 and the exposed source/drain regions or metal gateare exposed to nitrogen ions generated from the nitrogen containing gas56 to form a nitrogen enriched dielectric layer 55. The nitrogenenriched dielectric 55 can serve to provide a protection layer to theunderlying bulk dielectric material 52 so as to prevent dielectricdamage and minimize surface roughness from additional processing. Asdescribed above, generation of the nitrogen ions can be plasma orthermally generated, wherein the nitrogen ions penetrate into at least aportion of the dielectric layer 52, i.e., on the order of a fewAngstroms. FIG. 2C provides and enlarged sectional view of the nitrogenenriched dielectric layer and the bulk dielectric. It should be apparentthat the nitrogen enrichment may form a gradient.

In FIG. 2D, a titanium metal liner layer 60 is then conformallydeposited onto the patterned substrate including the exposed nitrogenenriched dielectric surfaces defining the contact and the source/drainor metal gate regions. The titanium metal liner layer may be depositedthrough conventional deposition processes such as, for example, a plasmavapor deposition process such as Rf sputtering. The thickness of thedeposited titanium metal liner layer is between 10 Å and 40 Å. Atitanium nitride layer 62 forms at about an interface of the titaniummetal liner layer 60 and the nitrogen enriched dielectric layer 55.

In some embodiments, it may be desirable to have the titanium metallayer directly contact the underlying metal gate structure as shown inFIG. 2E. For example, after the step shown in FIG. 2B, a H₂-containedchemical treatment is applied to selectively remove the nitrogenenriched layer from the bottom surface of the contact feature (S/D or MGsurface), while keeping the nitrogen enriched layer at sidewalls of thecontact feature.

Next, a conductive metal such as tungsten is then deposited into thecontact hole to form the so-called tungsten plug (not shown, but similarto that shown in FIG. 1D using a conventional deposition processincluding, but not limited to: CVD, PECVD, sputtering, chemical solutiondeposition or plating). By way of example, a conformal LPCVD procedureat a temperature between about 400 to 500° C. can be used to deposit thetungsten layer to a thickness between about 2000 Å to 9000 Å. Thereactants, as well as the by-products, of the tungsten deposition,performed using silane and tungsten hexafluoride, cannot attackunderlying materials, now protected by titanium nitride layer. Althoughtungsten is preferred, other suitable conductive materials include, forexample, Cu, Al, and combinations thereof. The conductive material isfilled into the contact hole.

A chemical mechanical polishing (CMP) procedure is next used to removethe regions of tungsten, and the regions of titanium nitride layerresiding on the top surface of ILD 12 such that the upper surface of thetungsten plug that is substantially coplanar with the upper surface ofthe dielectric material. In addition to removal of the unwanted regionsof material, via a CMP procedure, the removal procedure can also beaccomplished via a blanket RIE procedure (without the use ofphotolithographic procedures) using a suitable etchant

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are combinable with each other.

All cited patents, patent applications, and other references areincorporated herein by reference in their entirety.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Further, it should further be noted that the terms “first,”“second,” and the like herein do not denote any order, quantity, orimportance, but rather are used to distinguish one element from another.

While the preferred embodiment to the invention has been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

1. A contact structure for an integrated circuit device, comprising; apatterned dielectric material comprising at least one contact hole, thecontact hole including a bottom surface, and sidewalls extending fromthe bottom surface to a top surface, wherein the bottom surface isdefined by a source/drain region or a metal gate, wherein the bottomsurface and sidewalls extending from the bottom surface comprise anitrogen enriched surface on and in a portion of the patterneddielectric material; a metal nitride liner layer on the sidewalls andthe bottom surface of the at least one contact hole; and a tungsten plugdisposed within the at least one contact hole.
 2. The contact structureof claim 1, wherein the metal nitride liner layer is Ti(N).
 3. Thecontact structure of claim 1, wherein the metal nitride liner layercovers the bottom surface.
 4. A contact structure for an integratedcircuit device, comprising; a patterned dielectric material comprisingat least one contact hole, the contact hole including a bottom surface,and sidewalls extending from the bottom surface to a top surface,wherein the bottom surface is defined by a source/drain region or ametal gate, and wherein the patterned dielectric material comprises anitrogen enriched surface on and in a portion at least at the sidewallsof the contact hole; a metal liner layer disposed on the sidewalls andthe bottom surface of the at least one contact hole, wherein contact ofthe metal liner layer with the nitrogen enriched patterned dielectricmaterial forms a metal nitride gradient in the metal liner layer; and atungsten plug disposed within the at least one contact hole.
 5. Thecontact structure of claim 4, wherein the bottom surface of the at leastone contact hole is nitrogen enriched in addition to the sidewalls. 6.The contact structure of claim 4, wherein the metal liner layer is indirect contact with the source/drain regions or metal gate at the bottomof the contact hole.
 7. The contact structure of claim 4, wherein themetal nitride liner layer is Ti(N).